According to national and international regulations (e.g. EC recommendation 1999/519/EC and RTTE Directive 1999/5/EC), when a base station (BTS) is put into service, it is mandatory to comply with the essential safety requirements, in particular those related to human exposure to RF emissions. In-situ compliance assessment depends on the EM environment (EME). It is impacted by reflection and diffraction from nearby objects and by emissions from other sources (e.g. broadcast, FM . . . ) or from other mobile networks (GSM or UMTS). This problem is particularly important in a context of site sharing.
To date, operators or regulatory agencies have to make in-situ measurements to verify a posteriori that the EM environment has not changed since the base station has been put into service.
Usually a measurement equipment consisting of an electromagnetic field probe and a measurement device (e.g. a spectrum analyser or a voltmeter) which is controlled by a laptop is used for performing the electromagnetic field survey. By means of such a measurement, an accurate verification can be performed that the applicable electromagnetic exposure limits, which have been issued by the competent authority have been met. To date, exposure limits for the general public are defined by the European recommendation 1999/519/EC.
The methods for compliance assessment are defined by CENELEC (European Committee for electrotechnical standardisation, documents from TC 106X WG1) under the mandate M305 of the European Commission. Compliance assessment of a base station is performed according to the standards EN50383 to EN50385, when the equipment is put on the market. Compliance assessment when the base station is put into service is performed according to the draft European standards prEN50400 and prEN50401. European standards for market enforcement and in-situ measurements are currently being drafted. A large number of protocols have been established on a national basis (for example in France by Agence Nationale des fréquences 'in situ measurement protocol', edition 2001) or on an international basis (for example CEPT 02 04 “measuring non-ionizing radiation (9 kHz-300 GHz)” from the Electronic Communications Committee (ECC) within the European Conference of Postal and Telecommunications Administrations (CEPT)). In particular, those standards apply when a base station of a cellular telecommunication system is installed.
However, these norms also have to be met during operation of the base station, especially when the electromagnetic environment has changed. For this purpose, electromagnetic field exposure surveys are performed by the operators or the regulatory agencies. The disadvantage of this procedure is that monitoring of EME changes with a posteriori in-situ measurements requires a lot of manpower (cf. C. Olivier, L. Martens, “Measuring techniques for the exposure assessment around base stations for mobile communications”, Proceedings of the 9th URSI Forum 2001, 13 Dec. 2001, Louvain-la-Neuve, Belgium, pp. 5. C.; Olivier, L. Martens, “A practical method for compliance testing of base stations for mobile communications with exposure limits”, Proceedings of the 2001 IEEE AP-S International Symposium and USNC/URSI National Radio Science Meeting, Vol. 2, 8-13 Jul. 2001, Boston, Mass., USA, pp. 64-67; C. Olivier, L. Martens, “Measurements of exposure to electromagnetic radiation around GSM base stations in Belgium: a base for a practical measuring procedure”, Abstract book of the BEMS Twenty-Third Annual Meeting in cooperation with the European Bioelectromagnetics Association, 10-14 Jun. 2001, St. Paul, Minn., USA, pp. 102-104; W. Joseph, L. Martens, “Calibration of field probes and study of the disturbance on the evaluation of electromagnetic fields”, Proceedings of the 9th URSI Forum 2001, 13 Dec. 2001, Louvain-la-Neuve, Belgium, pp. 48.).
The present invention therefore aims to provide an improved method of monitoring a fixed transmitting station.